This invention relates to a bottom operable lading loading and unloading valve assembly for a railway tank car. For the most part tank car lading valves have been operable from the top manway of the tank. However, this is disadvantageous because of the danger of the operator falling off the car during loading or unloading. Furthermore, if the valve assembly is in some way defective or inoperative, or if the valve assembly requires cleaning, the operator must do so from the inside of the car. The lading must be removed from the car for this to take place. Working on the valve assembly inside of the car is often an expensive maintenance operation for the tank car owner or lessee, and there is some danger to the operator working inside the car.
Currently, the problem of derailments suggests that it would be preferable for the outlet mechanism to shear off upon impact rather than punch or tear a hole in the tank bottom. Therefore it is desired that there be readily shearable planes in the valve assembly which will shear off in the event of impact to the valve assembly. Furthermore, to the extent that the vertical operator will shear off below the tank a skid is not required. Avoidance of a skid reduces the cost and weight of the car.
It is particularly important, for example, during derailments to be able to replace a defective lower valve plug operating mechanism while the tank contains lading and the plug portion of the valve remains in place to prevent the lading from escaping.
Furthermore, leakage is always a problem and it is desired to provide a valve assembly design which will provide positive sealing to provide assurance against leakage.
One bottom outlet is disclosed in U.S. Pat. No. 1,565,913 (1925). In this patent a valve outlet assembly is riveted to the tank with rivets 16. A transverse operator 29 is utilized to move a valve member 24 into and out of engagement with a seat formed on cylindrical threaded housing 18. Operator 29 is rotatable, but is prevented from longitudinal movement. A stop 32 is provided which the valve engages in the full open position.
This patent requires a large outlet housing attached to lower portion of the tank, and includes a pair of valve assemblies to unload the car from opposite sides of the track.
Ball valves have been provided on tank cars which are operable from the bottom exterior of the tank. See, for example, U.S. Pat. Nos. 3,227,101 (1966); 3,591,131 (1971) and 3,661,355 (1972). These ball valves are quite expensive and it is desired to obtain a design which is less expensive than a ball valve.
Angle valves have also been utilized in tank cars. See, for example, page 3, 5 and 7 of the catalog REGO, RAILROAD TANK CAR VALVES, 4201 West Peterson Avenue, Chicago, Illinois. Copyright 1970, Rego Divison of Golconda Corporation. Angle valves utilizing a handwheel and a vertically extending threaded shaft cooperate with threads on the fixed housing to move the valve member between an open and closed positions. However, even if such an angle valve were reversed and used as an outlet valve (and there is no suggestion to do so) there is no teaching of the operating mechanism of the outlet shearing off under impact.
This same catalog on page 11 discloses a bottom operated discharge valve which is vertically movable within a strainer 4 and a housing 6 guides the vertical movement. A handle 20B is connected to an operating shaft 15B which is in turn connected to a cam lever arm assembly 16B which raises and lowers the valve without rotation. See also U.S. Pat. No. 3,199,534.
In Melott U.S. Pat. No. 2,002,672 (1935) a valve member 32 is provided with a stop 83 to limit travel of the valve in open position.
U.S. Pat. No. 2,567,426 discloses a wine bung screw valve including an external groove in the valve housing and rotatable and vertically movable operator to move a valve plug between open and closed positions.
In U.S. Pat. No. 2,072,271 (1937) a vertically movable safety valve utilizes guide members 32 to maintain basically vertical movement of the valve head B and prevent the same from being cocked during the vertical movement. However, this is a safety valve movable between open and closed positions against the bias of a spring by pressure from a pressure chamber. It has no operator in the sense of a manual operator for a discharge valve, and thus this valve is not adapted to be used as a bottom discharge outlet.